This application claims the benefit of Korean Application No. P2001-83245 filed on Dec. 22, 2001, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a backlight unit for a liquid crystal display device. The present invention is also directed to a method of assembling the backlight unit which makes it easy to inspect for impurities and reduces the damage to an optical sheet.
2. Description of the Related Art
Generally, a liquid crystal display device has a liquid crystal display panel consisting of a plurality of liquid crystal cells arranged in a type of matrix and a plurality of control switches for switching a video signal to be supplied to each liquid crystal cell, and for controlling the transmittance of the light supplied from a backlight unit with the liquid crystal display panel to display a desired picture on a screen.
When compared to a Cathode Ray Tube, such a liquid crystal display device is possible to be made in a small size so that it can be applied to Office Automation Equipment such as a photocopying machine, etc., and Potable devices such as a mobile phone and a pager, etc., as well as a personal computer PC and a notebook computer.
A light guide panel method is widely used as a backlight unit, which supplies light to the liquid crystal display device, since it is required to make the screen of the liquid crystal display device bigger in size, better in displaying color and more elegant in appearance.
Accordingly, there has actively been carried out research and development for high and uniform brightness, thinness and lightness of a backlight unit.
Referring to FIG. 1, a backlight unit of a conventional liquid crystal display device includes a lamp assembly 10 consisting of a lamp 10a for generating light and a lamp housing 10b installed in the shape of a cover for lamp 10a; a light guide panel 14 for converting the light incident from the lamp assembly 10 into a planar light source; a reflection plate 12 located at the bottom thereof for reflecting the light, which progresses toward a lower surface or a side surface of the light guide panel 14, to an upper surface; a bottom cover 20 installed under the reflection plate 12; optical sheets 16 for diffusing the light passed through the light guide plate 14 and controlling the direction in which the light progresses; and a main support 18 mounted on the optical sheets 16.
A cold cathode fluorescent lamp CCFL is mainly used for the lamp 10a. The light generated in the lamp 10a is incident to the light guide panel 14 through an incidence surface in the side surface of the light guide panel 14. Two or three lamps 10a can be installed to achieve high brightness of the liquid crystal display device. The inside surface of the lamp housing 10b has a reflective surface for reflecting the light from the lamp 10a to the light guide panel 14. The reflection plate 12 is installed facing the rear of the light guide panel 14. The light guide panel 14 receives the light incident from the lamp 10a to reach a long distance from the lamp 10a. The light guide panel 14 is normally formed of an acrylic acid resin PMMA, which has good strength so as not to be easily deformed or broken while providing good transmittance. The reflection plate 12 reflects the light incident to itself through the rear of the light guide panel 14 toward the light guide panel 14, thereby reducing light loss. The light transmitted to the lower surface and the side surface of the light guide panel 14 is reflected at the reflection plate 12 and progresses toward the surface of the light guide panel 14 from which light emanates. The bottom cover 20 is located under the reflection plate 12 for supporting the components of the backlight unit on the bottom cover 20.
The optical sheets 16 is composed of a first diffusion sheet, a first and a second prism sheet for controlling the progress direction of the light passed though the first diffusion sheet, and a second diffusion sheet for diffusing the light passed though the first and the second prism sheet. The light passing through the light-emanating surface of the light guide panel 14 is incident to the first diffusion sheet among the optical sheets 16 to be diffused. On the other hand, when the light is perpendicularly incident to the liquid crystal display panel (not shown), it has a higher light efficiency. For this, two forward prism sheets are deposited for the progress angle of the light coming out of the light guide panel 14 to be perpendicular to the liquid crystal display panel. The light passed through the first and the second prism sheet is incident to the liquid crystal display panel via the second diffusion sheet.
A main support 18 is a major supporting part of the backlight unit and supports the whole of the backlight unit and the liquid crystal display panel.
In conjunction with FIG. 2, there is explained below a method of assembling the backlight unit with such a configuration.
Referring to FIG. 2, the backlight unit is assembled in reverse direction, and first of all the optical sheets 16 are disposed on the main support 18, and the first diffusion sheet, the two prism sheets and the second optical sheet are sequentially deposited on the main support 18. Then, the lamp assembly 10 and the reflection plate 12 is combined to both sides of the light guide panel 14. The reflection plate 12 is mounted on one surface of the light guide panel 14 and inside the lamp housing 10a. The light guide panel 14 combined with the lamp assembly 10 and the reflection plate 12 in this way is then assembled on the optical sheets 16. Then, after the bottom cover 20 is mounted on the light guide panel 14, the wiring of the backlight unit is adjusted for supplying voltage generating a light to complete the backlight unit. An liquid crystal display panel is assembled to the backlight unit assembled in such a way.
If the backlight unit is assembled in a reverse direction, it is not possible to inspect for impurities generated in the course of its assembly. That is, while the inspection of generated impurities can be carried out through a lighting inspection, the light assembly 10 being the light source required for the lighting inspection is assembled after the optical sheets 16 are assembled. Accordingly, because the lighting inspection is carried out after the optical sheets 16 have been assembled, it becomes difficult to eliminate the impurities generated at the optical sheets 16. Therefore, a JIG that irradiates light for inspecting whether or not impurities is generated, is separately required. Also, when assembling the backlight unit in the reverse direction, because the optical sheets 16 are deposited on the main support 18 before anything else, damage of the optical sheets 16 is likely. Moreover, because the wire of the backlight unit is long, it becomes difficult to adjust the wire at the end of the assembly. Thus, there arises the necessity of a new assembly method of the backlight unit to solve these problems.